1. Field of the Invention
The present invention relates to computer pointing devices and, more particularly, to transfer functions for use in conjunction with computer pointing devices.
2. Related Art
Conventional computing devices typically accept input from input devices such as a keyboard and/or a pointing device, such as a computer mouse. A typical computer mouse, which is shaped to fit underneath a user's cupped hand, may be moved laterally by the user over a flat surface (such as a mouse pad or a desktop), thereby causing corresponding changes in the coordinates of a pointer (such as an arrow icon) on the computer screen (referred to herein as an “on-screen pointer”).
The input provided by a pointing device may be represented by an input vector having a magnitude and a direction. The input vector obtained from a mouse, for example, specifies both the distance and direction of the mouse's most recent movement. Software executing on the computer translates this input vector into an output vector specifying the distance and direction in which the on-screen pointer is to move. The output vector is generated from the input vector using a transfer function, which defines the relationship between input vectors generated by the mouse and corresponding output vectors. Transfer functions, such as those associated with computer mice, which relate input distance or coordinates to output distance or coordinates are referred to as “positional” transfer functions, and the devices that use them are referred to as “positional” pointing devices.
Trackpads, which are often used in laptop computers, are another example of a positional pointing device. A laptop trackpad typically includes a small and flat surface that is positioned just below the keyboard. Moving one's finger across the surface of a trackpad causes the on-screen pointer to move in a corresponding direction and by a corresponding distance that is proportional to the distance moved by the user's finger. In practice, the magnitude of the output vector is typically scaled upward so that the user may cause the on-screen pointer to move a relatively large distance by moving his finger only a small distance.
In contrast to positional pointing devices, pointing devices which relate input force to output (pointer) velocity are referred to as “velocity-based” pointing devices, and the transfer functions they use are referred to as “velocity-based” transfer functions. The IBM TrackPoint is one well-known example of a velocity-based pointing device. The TrackPoint includes a small nub typically nestled between the G, H, and B keys of a laptop computer. The user applies lateral force to the nub in the direction in which pointer movement is desired. Although the nub itself does not move perceptibly, it senses the direction and amount of force applied by the user's finger and causes the on-screen pointer to move in the same direction and with a velocity that is proportional to the magnitude of the applied force. The user may, therefore, speed up movement of the pointer by applying more force and slow down movement of the pointer by applying less force.
Conventional positional pointing devices are best used when fine-grained control over pointer position is required. To enable the pointer to be moved easily over large distances, however, a pointing device having a large range of movement is required. This can be problematic because a large range of movement requires either a large pointing device (as in the case of trackpads) or a large area within which to move the pointing device (as in the case of computer mice). It is therefore particularly difficult to implement positional pointing devices having a large range of movement for use with small, portable, computing devices such as laptop computers or personal digital assistants (PDAs).
Although velocity-based pointing devices may enable the user to move the pointer over a large distance without requiring a large range of movement, it typically is difficult to quickly position an on-screen pointer precisely using a velocity-based pointing device. Moving the pointer too quickly using a velocity-based pointing device may result in the pointer “over-shooting” the intended target. Although the pointer may be positioned more precisely by applying less force, thereby decreasing the pointer's velocity, using such a technique may significantly slow down the process of positioning the pointer at the desired coordinates.
What is needed, therefore, are pointing devices which provide flexible control over the position and/or velocity of an element such as an on-screen pointer.